Upgrade guide from v1?

[fatso83]

I have inherited an older Symfony 3.4 project with a dependency causing issues with PHP 8:

php.CRITICAL: Type error: implode(): Argument #2 ($array) must be of type ?array, string given {"exception":"[object] (Symfony\Component\Debug\Exception\FatalThrowableError(code: 0): Type error: implode(): Argument #2 ($array) must be of type ?array, string given at /home/my-user/code/ACME-api/vendor/friendsofsymfony/jsrouting-bundle/Extractor/ExposedRoutesExtractor.php:202)"} []

It's the ancient 1.x version of "friendsofsymfony/jsrouting-bundle": "1.*"

Naturally, I would like to upgrade it (seems like 2.8 should be doable), and from the README it seems as this is the successor the 1.x version, but I fail to see a migration guide. Is there one?

Upgrading this will be quite a handful, seeing I also depend on this 8 year old Angular 1.x plugin 🙈